Recurrent mutations have been reported in MAP2K1, TP53, U2AF1, KMD6A, CREBBP, and ARID1A. MAP2K1 mutations have been found in about 30% of SBLPN/HCLv [57, 59–62] and since they are only rarely found in SMZL and SDRPL, they can help in the differential diagnosis [24, 50]. Here, ARID1A is linked to splenic diffuse red pulp small B-cell lymphoma.